Conventionally, as the submerged membrane separator of this type, there has been a submerged membrane separator that is submerged in a treatment tank to separate activated sludge and treated water, as shown in FIGS. 28 to 30. A submerged membrane separator 1 includes a box-type casing 2 opened at the top and the bottom, a plurality of vertically elongated membrane cartridges 3 arrayed in parallel to one another in the casing 2, and an air diffuser 4 provided below the membrane cartridges 3.
Water intake nozzles 6 for sucking treated water 5 obtained by membrane filtration are provided on the upper end sides of the membrane cartridges 3. A plurality of slits 12 elongated in the up-down direction are formed on the left and right inner side surfaces of the casing 2. The membrane cartridges 3 are held in the casing 2 at predetermined intervals with both sides of the membrane cartridges being inserted into the slits 12 from above.
Water collecting pipes 8 for collecting the treated water 5 are provided on one side of an upper opening 7 of the casing 2. The water collecting pipes 8 and the water intake nozzles 6 of the membrane cartridges 3 are connected via connection pipes 9. A lead-out pipe 15 for leading out the treated water 5 is connected to the water collecting pipes 8. A suction pump (not shown) that generates a suction force for sucking the treated water 5 is provided in the lead-out pipe 15. A suction force may be generated by using a water head pressure of a liquid to be treated in a treatment tank as a filtration driving pressure without using the suction pump.
With this configuration, during a filtration operation, the inner sides of the membrane cartridges 3 are depressurized by the suction pump or the like while air is diffused from the air diffuser 4. Thus, sludge or the like in a liquid to be treated 11 is caught by filtration membranes 10 of the membrane cartridges 3. A liquid permeating through the filtration membranes 10 and flowing into the inner sides of the cartridges 3 is collected as the treated water 5 in the water collecting pipes 8 from the water intake nozzles 6 through the connection pipes 9, and is removed from the water collecting pipes 8 through the lead-out pipe 15.
In this case, upflow 13 is caused between the membrane cartridges 3 by bubbles of air diffused from the air diffuser 4. The matter adhering to the membrane surfaces of the membrane cartridges 3 is removed by this upflow 13.
When the membrane cartridge 3 is removed in maintenance or the like, after the filtration operation is stopped and the liquid to be treated 11 in the treatment tank 16 is discharged, as shown in FIG. 28, the membrane cartridge 3 is pulled out from the upper opening 7 to above the casing 2.
Since the air is diffused from under the membrane cartridge 3, the longer the filtration membrane 10 becomes in the top-down direction, the more effectively the air diffusion can be used. As a result, it is desirable to form the membrane cartridge 3 in an elongated shape (a rectangle) as shown in FIG. 28.
The submerged membrane separator 1 having the above-described configuration is described in, for example, Japanese Patent Application Laid-Open No. 2001-87763.